Surgery for grafting of the coronary arteries has most commonly been done using cardiopulmonary bypass with the heart stopped. Recently, the advantages of avoiding the blood damage caused by the heart lung machine have been recognized, and a number of methods to operate on the coronary arteries without using oxygenators have become more common. The patient""s natural heart or some type of heart assist device is used to pump the blood through the body and through the lungs. In some operations, particularly when the heart must be lifted or displaced to gain access to the site of a coronary artery graft anastomosis, the flow through the heart may be diminished due to kinking of the atria or blood vessels directly adjacent to the heart.
In the case of kinking of the inflow to the right side of the heart, blood flow across the lungs will be diminished, which in turn will diminish filling of the left side of the heart which will decrease cardiac output.
The present invention provides a very simple and inexpensive device and method to maintain the cardiac output even while the inflow to the right side of the heart is kinked or obstructed by compression. A passive shunt from the right heart inflow to the pulmonary artery is created which is opened during the time when the natural right inflow is blocked. The preferred embodiment includes an inflow cannula and a pulmonary artery cannula, and a tube connecting them containing a flow actuated valve to prevent back flow from the pulmonary artery. A portion of the tube is adapted to be clamped to shut off the flow completely. The preferred placement is with the inflow cannula in the inferior vena cava and the outflow cannula in the pulmonary artery. The inflow cannula may include side holes adapted to permit blood from the right atrium (originating from the SVC and coronary sinus) to also enter it.
During use, the shunt is placed and either clamped or left so that pressure from the pulmonary artery closes the valve. The patient is then given a sufficient volume of fluid so that his/her right atrial pressure is elevated [above normal] to about 25 mmHg. When the heart is manipulated during surgery and the right inflow is obstructed, the clamp is removed and blood will flow passively through the shunt to bypass the obstruction. This will maintain sufficient blood across the lungs to supply the left heart and maintain the patient""s arterial blood pressure.
Alternative embodiments of the shunt include a model with no valve, in which case the surgeon must attend to clamping and un-clamping the shunt as necessary, and another embodiment having two valves and a compressible chamber between them, adapted to be squeezed manually to provide a hand actuated right heart bypass pump.
It is an object of the present invention to provide a device to bypass the right heart during surgical manipulation.
It is a further object of the invention to provide a valved right heart bypass shunt adapted to prevent back flow from the pulmonary artery when the right ventricle is receiving sufficient filling to pump effectively, and automatically act as a shunt when the right heart filling is obstructed.
It is another object of the invention to provide a method to permit surgical manipulation of the heart using a passive right heart bypass shunt.
It is a still further object of the invention to provide a simple, inexpensive right heart bypass pump which is manually actuated by the surgeon during brief periods of use while the natural heart is surgically manipulated.
It is another object of the invention to provide a passive right heart shunt which may be used in conjunction with a left heart assist device so as to maintain the pulmonary circulation even at times when the right heart inflow is obstructed.